I have a grid column which can display numbers ranging from single digits and into the billions. I think that at some point we need to switch from displaying the whole number to using abbreviations, like 7M for millions or 2B for billions, like discussed in What is an alternative way to display a very large number?.

The question is at what point do we switch, since I would like to keep the order of magnitude easily recognizable at first glance, so I wouldn't want to have thousands, millions and billions all represented by characters (10K, 10M and 10B all look the same at first glance). Are there any conventions on this? Maybe from financial apps?

Do the numbers appear in a random order, or is the list ordered by the number? What sort of precision (how many significant digits) do you need to retain?
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Andrew LeachJul 26 '12 at 6:59

@dnbrv They're ok with the existing format (no abbreviation), but we'd like to make it more than ok :).
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Vitaly MijiritskyJul 28 '12 at 6:00

@AndrewLeach It's a grid, so it can be sorted by this column or by any other column, and then this one appears in a random order. As to precision - we need to know which row is higher, and to have a good idea about the order of magnitude.
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Vitaly MijiritskyJul 28 '12 at 6:02

5 Answers
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I think this depends greatly on the context of the data and what your users expect to do with it. If, for example, you're dealing with financial data in tables (as in an invoice), there are obvious reasons why you'd want to preserve positional numbers/tabular figures (to allow you to compare like-with-like easily).

If information fidelity/accuracy is less important (where simple magnitude will generally suffice), using abbreviations makes a lot of sense. This is true in operating systems' representation of file sizes, where any a given folder could have files that are very large and very small.

Here's how that's shown in OS X Lion:

As you can see, this folder contains files varying in size from 689 bytes to over 3 GB. This same information, presented in absolute terms (bytes only) looks like this:

As you can see, this latter option gives a much better idea of the relative sizes of things just by their width. The issue is we don't generally talk in terms of bytes (any more); most of the files we send around are at least a few kilobytes and often larger than a few megabytes. Since people talk in those terms, it makes sense to display the information the way users will best understand it and interpret it. It's also true that nowadays (with very large hard drives being ubiquitous) we don't often have a need to do file size comparison (and with the ability to sort the list in size order, we can quickly do so if actually required).

While I know it's not your actual scenario, I figure it's worth noting that most journalistic institutions provide style guide recommendations for when to use which representation for numbers, mostly intended to ensure figures can be easily compared.

Sadly good online style guides are few and far between (they tend to be printed resources, and I don't have them with me here to quote from), but they tend to specify different rules for monetary amounts, numbers of people and percentages or other such figures.

Can you add some subtle colouring, to enhance the perception of the differences? So K, M and B values are all slightly different colours? This can help the user to percieve a difference and then therefore not the differences. It is not easy to get this right, but it might be a possibility.

Could you display K as they are, M as M and B as Bn. The would mean that there are only two symbols to recognise, which are different lengths (M and Bn)? Bn is used for billions sometimes, so should be recognisable.

However, as per @dnbrvs comment, you need to work out what the users would feel happiest with. What do they currently use to differentiate between these scales of numbers, and can you utilise this in your design?

I've spent several years working on a financial/statistical system that reports on monetary values (and other numbers) from units through trillians, so perhaps similar to your needs. That system works like this (simplified):

Values are shown to at least 3 significant figures, using standard suffixes for magnitude.

The number shown is never < 1 nor >= 1,000 - if this were to happen, the next suffix is used instead

I can't add a comment because my rep score is too low, so I'll just add it as an answer. One additional thing you should keep in mind as you start to use abbreviations (M, B, etc.) or words (million, billion, etc.), is the cultural differences in number scales.

We in the US use the short scale, where each new name past million is 1000 times the magnitude of the previous name - 1 billion is a thousand millions; 1 trillion is a thousand billions. However, much of continental Europe and other places use the long scale, where each new name past million is a 1000000 times the magnitude of the previous name - 1 billion is a million millions, 1 trillion is a million billions. Many asian countries use different systems entirely - I know Japan's counting system is based on multiples of ten thousand until you get into very large numbers.

If your application isn't multinational, then it doesn't matter so much, but if it is then this can be very important, and is worth some research before implementing a solution that could cause very disruptive confusion.

Wikipedia has a great article explaining the differences, and listing which countries use which scales.

You could use scientific notation (n x 10^4) but that would not give you the precision you might need. I'd be inclined to right justify your numbers so it's easy to compare, or (if the data allows) to group by size.